Control means for radio landing systems



ec. 6, 1938. G. H. WINTERMUTEET A1. 2,1399@ CONTROL MEANS FOR RADIOLANDING SYSTEMS 2 sheds-sheet 1 Filed July 29, 1936 Dec. 6, 1938. G. H.WINTERMUTE E-r Al. 2,139,051

CONTROL MEANS FOR RADIO LANDING SYSTEMS 2 Sheets-Sheet 2.

O I q mw .Gwmm WQ WQ @0N T l a L. 25W@ 2h@ Y mn NWIN m Patented Dec. 6,1938 CONTROL MEANS Fon Ramo LANDING SYSTEMS Gerald H. Wintermute,New-ton, N. J., and Gomer L. Davies, Cleveland, Ohio, assignors toWashington Institute of Technology, Inc., Washingington, D. C., acorporation of Delaware Application July 29, 1936, Serial No. 93,280

17 Claims.

This invention relates to radio landing systems for aircraft, of thetype employing a localizing beacon for guiding the landing aircrafttoward a pre-determined area on the ground, such as an airport runway,and a landing beam which provides an upwardly-curved path in spacehaving its origin above, below or in the ground surface and at the endor in the prolongation of the runway, and which provides a path toground for the landing aircraft.

More particularly, the invention relates to a means for controlling theoperation of the transmitters which set up the various radiation fieldswhich denne or create ,the paths formingl the landing system, so that ifthe spatial or directional characteristics of the paths vary or changeso that an incorrect path to ground is defined thereby, the transmitterinvolved will be deenergized. The importance of such a'control will beevident when it is considered that, in periods of low visibility or novisibility and in making blind landings, the pilot of an aircraft whichis landing with the aid of the system, must rely entirely uponinstrument indications of the position of the aircraft with respect tothe various paths of the landing system in bringing the plane to earth.These indications show the lateral position of the plane with respect tothe airport runway and the position of the plane with respect to thecurved landing beam, and in the proper landing of the plane, undertheconditions reierred to, the pilot must rely upon the proper shape anddirection of the paths of the system.

Obviously, if the landing beam, for example, provides an improper pathto ground, a situation of great danger to the landing aircraft andpersons thereon is created. However, under the conditions referred to,the pilot has no means of knowing Whether the operation of the system issuch as to provide a proper path to ground and must assume that such isthe case if the aircraft instruments show the various beams of thelanding system to be in operation. In the event that, for any reason,the path to ground provided by the landing system is incorrect or out ofplace it will be preferable to de-energize that part of the system whichis not operating properly, in order that if the aircraft instrumentsshow that the landing system is operating, the pilot will knowabsolutely that the operation thereof is correct and that by properlyfollowing his instrument indications he will cause his plane to follow acorrect path to ground. Further, it is imperative that the operator ofthe landing system be warned means to an eifective and useful landingsystem` (Cl. Z50- 11) when the transmitting station ls de-energized oris operating improperly in order that he may make the necessaryadjustments or repairs, and may advise the pilot of the landing aircraftby radio or other means that one or more elements of the landing systemis not operating, in order that the pilot of the landing aircraft mayknow the operating condition of the ground equipment and will know whatindications to expect.

It is therefore the object of this invention to provide means formonitoring or controlling the various radiation fields of an aircraftlanding system in such a manner that if, for any reason whatsoever, theoperation of the system is not such as to provide a correct andpredetermined path to ground, the operation of the affected transmittingmeans which sets up the improper radiation field will be stopped, inorder that a correct path to ground or none at all will be provided bythe system.

Another object is to provide means for indicating at the transmittingpoint or at any remote station, the condition of energization orde-energlzation of the various transmitters of the system.

Other objects and features of novelty will be apparent from thefollowing description .i 1d the annexed drawings, wherein is disclosed asystem according to the present invention. It is to be understood,however, that the invention is in no way limited by such description anddrawings or otherwise than by the appended claims.

Figure 1 of the drawings shows diagrammatically the connections andelements of parts of the landing system and the control means thereforaccording to one form which the present invention may take;

Figure 2 of the drawings discloses an alternative. form of relay controlmeans which may be employed, and

Figure 3 discloses a system which may be employed for remote operationof the monitor system.

Radio landing systems of the type illustrated in connection with thepresent application comprise two principal guiding means, these being a.runway localizing beam for guiding the aircraft to the proper airportrunway, and a landing beam which provides an upwardly curved path havingits origin. at the transmitting antenna which is on or adjacent to theground surface and which beam deiines a proper path to ground for thedescending aircraft. 'Both of these means are adapted to be controlledby the control means according to the present invention. The landing ofthe position of the aircraft with respect to the edge of the landingeld, and such marker beacons may be controlled within the broad scopeofthe present invention. v

The runway localizing beacon which forms part of the system describedabove is defined by the intersecting area of two electric fields set upby the radiations from two antennasarranged on the ground. Preferably,the antennas are so energized as to radiate two overlapping fields eachhaving a iigure-of-eight radiation pattern, although intersectingcardioid field patterns may be employed if desired. The two fields arepreferably radiated at equal carrier frequencies and the carrierradiated from each antenna is given a characteristic modulation in orderto distinguish between the two radiated fields. It will be seen that inthe overlapping area the modulations impressed upon the radiation fieldsfrom the two antennas will be equal and that this equi-signal zone willhave directional characteristics and may therefore be employed as aguide or beacon. The radiation fields of the two antennas may bemodulated by alternate non-continuous signals such as the A and N'or Aand I signals for providing an aural indication in the aircraft, orcharacteristic continuous modulations may be impressed on the tworadiated carriers, in the manner first disclosed by T. E. Brockstedt inPatent No. 1,865,826. The latter type of modulation is usually employedwhen a visual type of aircraft signal is desired, although the A and Nor A and I signals may be converted to visual indications in the planeif desired.

The transmitting means for setting up the radiation fields dening therunway localizer beacon are shown generally at I in Fig. 1 of thedrawings. This transmitting means comprises a directive antenna array,the two crossed loop antennas 2, 3 being disclosed in the systemillustrated in Fig. l, each of these being supplied withcharacteristically modulated carrier from transmitter 4. In thepreferred operation of the system the antenna 2 is supplied with radiofrequency current modulated at a continuous audio frequency of `65cycles, while the antenna 3 is supplied with radio frequency currentmodulated at a continuous audio frequency of 86.7 cycles. The radiationfields produced by the antennas 2 and 3 are directional and arepreferably of iigure-of-eight form and intersect or overlap each otherto provide an equi-signal zone which may be aligned with the airportrunway and which defines the directional course for the aircraft tofollow.

The means for establishing a line of constant field intensity in'space,defining a path to ground along which the aircraft may descend, is showngenerally at 5 in the drawings and constitutes a transmitter 6 whichsupplies an antenna 1 with It will be understood that the specific meanso'r circuits for establishing either the runway localizer beacon or thelanding beam form no part of the present invention and that any suitablemeans for establishing these elements of the landing system may beemployed without departing from the present invention.

The runway localizer transmitter is supplied with power through leads,I0, Ii which are connected at I2 and I3 respectively, to main powerlines I4, I5 which may be connected to a source of power through alinestarter switch, not shown.

predetermined value.

A control switch I6 is inserted in the leads I3, II adjacent thetransmitter 4 to provide a manual control for such transmitter withoutaecting other parts of the system. Included in the leads I0, II are alsotwo relay contacts I1, I3, which form part of a relay I9 and each ofwhich may be operated to open position by means of the solenoid I9a ofthe relay to thereby open the circuit energizing the transmitter 4. Oneterminal of the solenoid Ia is connected to power supply line I4 atpoint I3, while the other terminal of the winding may be connected tosupply line I5 through lead 20, either of relay contacts 2Ia or 22a ofrelays 2I and 22. lead 23, lead 24, switch 12 and the armature 25 of atime-delay relay 26. The relays 2| and 22 are normally so energizedduring the operation of the system that the relay contacts 2 Ia and 22aare open, as will be described more fully hereinafter, and the circuitthrough winding I9a will consequently be normally open, therebyhormallymaintaining relay contacts I1 and I8 closed and permitting the supply ofpower to transmitter 4.

The winding of the time-delay relay 26 is connected directly across thesupply lines I4, I5 so that the relay will be energized a pre-determinedtime after power is connected to main power lines I4 and I5, therebycausing the armature 25 of the relay to connect the lead 24 to supplyline I5.

The manually operable switch 12 is provided for disconnecting themonitoring system from the power supply and cie-energizing the same,with'- out affecting the transmitters or the signal means.

The relay 2I comprises, in addition to the solenoid 36, the contacts 2Iawhich are controlled by the solenoid. The relay 2I is normally soadjusted that the movable contact 33a. thereof is 4 held out of contactwith iixed contact 2Ia,l by current in winding 36 butcis adapted andadjusted to move into engagement with contact 2Ia upon decreaseof thecurrent in winding 36 below a The relay 22 which includes the winding31, comprises also the fixed contact 22a and the movable contact 33h.The arrangement of this relay is such that upon in- -crease of thecurrent in winding 31 above a predetermined value the movable contact33h will engage contact 22a.

Means are provided by the invention for controlling the relay I9 and forcausing the same to be normally de-energized whereby the supply ofcurrent to transmitter 4 will normally be uninterrupted, such meansbeing operable to permit continued operation of the transmitter so longas the radiation fields produced by the antennas 2, 3 are such as toestablish an equi-signal zone ciening a pre-determined path in a properposition and direction with respect to the landing field. Such means areillustrated in the drawings and comprise the two plates 3|, 32 which arearranged locally with respect to the loops 2, 3 respectively and each ofwhich is capacitatively coupled to one of the loops to receiveradiations therefrom. If desired, coils inductively coupled to the loops2, 3 may be employed in place of the plates 3l, 32. The plates 3|, 32are connected to the two grids of a detector tube 33, which receivespower from a monitor supply unit 34 which is connected to the main powersupply lines I4, I5. The detected currents delivered by the two platecircuits of tube 33 are supplied to the grids of a rectier tube 35 whichis also supplied with power from the monitor power supply 34. The biasvoltages of the grids of tube 35 are independently In the normaloperation of the beacon, audio frequency voltages, of frequencies equalrespectively to the two radiated modulation frequencies, are supplied tothe grids of tube 35, and the currents taken by the plates of tube 35will be controlled by these grid voltages. It will be seen -that if thecurrents taken by each of the plates of tube 35 should be equal thevoltage drops across the equal resistors a and b will be equal and bothplates of tube 35 will beat the same potential and no current will owthrough the series-connected windings 3B, 31 of the relays 2|, 22 whichare connected across the plates of tube 35. In the operation of the,system the potentiometers 34a and 34h are so adjusted that the plates oftube 35 will not take equal currents. When this condition obtains apotential difference will exist between the two plates of tube 35 and acurrent will ow through the relay coils 36 and 31. Relay 2l is adjustedto operate on a slightly lower current than relay 22. With normal andproper beacon operation the unbalance of tube 35 is so adjusted thatrelay 2l operates, thereby opening contacts 2Ia, while the unbalance isinsufiicient to operate relay 22. In the event of any variation in thecurrents in antennas 2, 3, the degree of unbalance of tube 35 willchange. If the change is such that more current flows through coils 36,31 the relay 22 will operate, closing contacts 22a, while if the changeis such that less current ows in the coils, the relay 2| will release,thereby closing contacts 2 Ia.

Each of the contacts 2Ia, 22a is connected to one terminal of windingISU, of relay I9 through lead 2B while the movable contacts 38a and 38hare both connected to main power supply line I through leads 23 and 2S.and armature 25 of the time-delay relay 26.

It will be seen that so long as the energy introduced into the plates 3iand 32 due to capacity coupling between the plates and the transmittingantennas 2,v 3 respectively does not decrease or increase above or belowpre-determined limits the movable Contact members 38a and 33h will bemaintained out of engagement with fixed contact 'members Zia and 22a andthe circuit through winding ISa of relay I9 will therefore be open,deenergizing the relay l@ and permitting the relay contacts I1, i8 topass current from the power supply lines to transmitter d.

Inasmuch as the field pattern of the radiation from either of theantennas 2, 3 and the position and direction of the equi-signal zone arefunctions of the current flow, in the antennas, it will be seen that anyincrease or decrease of the current in one of the antennas 2, 3, ortotal de-energization of one of the antennas will cause the coursedefined by the radiation elds of the antennas to shift from thepredetermined position to a position giving an improper directionalindication to a landing aircraft. For this reason, it is preferable tocompletely de-energize the affected transmitter when either of theradiation elds of the antennas 2, 3 varies from the predetermined shape.

When the current in the windings 36, 31 decreases below a predeterminedvalue by reason of the change of the potential difference between theplates of tube 35, the relay contact 2Ia will be closed by release ofthe movable contact 38a and the above-described circuit through relay I9will be completed and relay contacts I1, I8 will be opened, therebydisconnecting transmitter 6 from the main supply lines Id, I5 andde-energizing the transmitter. Further, when the current in the windings36, 31 increases above a predetermined value, due to a change of thepotential difference between the plates of tube ,35, the relay contact22a will be closed by movement of the movable contact 38h and theabove-described circuit through relay I9 will be completed and relayVcontacts I1, I8 will be opened, thereby disconnecting the transmitter 4from the power supply lines I6', I5. The relay contacts I1, I8 will notbe returned to closed position to permit operation of the transmitteruntil manually re-set. By reason of the above-described operation 4itwill be seen that transmitter 4 will operate to provide radiation eldsdening a runway-localizing equisignal zone or beacon only when theradiated lfields from antennas 2, 3 are such as to provide thepredetermined path.

Means are provided by the invention for indicating when the runwaylocalizer transmitter is connected to the main powerlines I8, I5 throughrelay contacts I1, I8 and when the monitor system therefor is operatingproperly. Such means comprise a signal 40 for indicating that themonitor system for the runway localizer transmitter has not yet goneinto operation or that the transmitter 4 has been disconnected from thesource of power. This signal may be either aural or visual in type butis preferably a red visual signal. signal 4I which is preferably a greenvisual signal and which, when energized, indicates that the monitorsystem for the runwaylocalizer transmitter is operating properly andthat such transmitter is connected to the source of power and isoperating in a proper predetermined manner. One terminal of each of thesignals 6D and 6I is connected by lead 39 to main power supply line atpoint I2. The other terminals of signals 40 and Si are connectedrespectively to two fixed spaced contacts 42, 63 between which andmovable into engagement with either is a movable contact 44. The movablecontact M is normally in engagement with iixed contact 42 of the redsignal 60 but is adapted to be moved into engagement with xed contact 53of green signal @I upon energization of the solenoid of a relay denotedgenerally at 55, and which is provided to control the movement ofcontact member M.

' The relay l5 comprises the winding IlS, one terminal of which isconnected to main power supply line Iii, through lead 131, lead l I,relay contact l1 and connection I3. The other terminal of winding 16 isconnected to main power supply line I5 through lead '38, lead 2d, andarmature 25 of timedelay relay 26.

It will be seen that if the switch I6 is closed, the connection of mainpower supply lines Ill, I5 to a source of electric energy will cause thetransmitter l to be energized and will also supply current to red signallil through lead @9, movable contact del, and fixed contact L32. therebyenergizing the red signal and indicating that the monitor system for therunway localizer transmitter is not yet operating. After a predeterminedinterval following the connection of main power supply lines to thesource of energy, the time-delay relay 26 will operate, and the armature25 thereof will move to connect lead 2Q to main power supply line I5. Ifthe radiations from transmitter 4I are proper and define a predeterminedpath,A

so that the relay I9 is de-energized, and if the switch I6 is closed,the operation of tite timedelay relay 26 will connect the winding 46 ofrelay 'l5 across the main power supply lines I4, I5, therebyrenergizinfgthe relay and causing The signal system also includes amovable contact 44 to move out of engagement with fixed contact 42 andinto engagement with xed contact 43. The red signal 4I) will accordinglybe de-energized and the green signal 4I will be operated to indicatethat the transmitter 4 is operating properly and in a predeterminedmanner and that the monitoring system is operating properly to controlthe operation of the transmitter. conditions of the radiations fromantennas 2, 3 are maintained, and so long as the monitoring systemoperates properly, the circuit through relay 45 will remain energizedand the green signal 4| will be operated.

When, by operation of manual switch I6 or by automatic opening of relaycontact I 1 by relay I9, the transmitter is disconnected from the mainpower supply lines, the circuit through winding 46 of relay 45 will bebroken and the movable contact member will move from contact with relaycontact 43, thereby de-energizing the green signal 4I, and will moveinto contact with the relay contact 42, thereby energizing the redsignal 40 and indicating that transmitter 4 is disconnected from thepower supply and that radiation from antennas 2, 3 has beendiscontinued.'

As set forth herelnbefore thelanding system comprises, in addition tothe runway localizing beacon, an upwardly curved path in space havingits origin at the ground and being constituted by a line of constantiield intensity in the field radiated from a transmitter located on orad` jacent to the surface of the ground. The 'means for setting up thisradiated iield is denoted genv erally at 5 in the drawing and comprisesa transmitter 6 which supplies properlymodulated radio frequency currentto an antenna 1. The transmitter 6 is connected to the main power supplylines I4, I5 through leads 50 and 5I respectively, the lead 56 beingconnected to main power supply line I4 at point I3 and the lead 5| beingconnected to the main power supply line I5 at point I2. A relay 52 isprovided for controlling the connection of transmitter 6 to the mainpower supply lines and such relay includes the contact members 53 and 54which are included respectively in the leads 50 and 5| and which areoperable by the solenoid 55 of the relay 52 to open or close the circuitto the transmitter 6. A manually operable switch 56 is also included inthe circuit tol the transmitter 6 for the purpose of manuallycontrolling the operation of the transmitter. The relay contacts 53, 54are normally closed, thereby permitting the supply of power to thetransmitter 6 and these switches are adapted to be opened uponenergization of relay 52 in order to disconnect the transmitter 6 fromthe power supply lines.

The means for controlling the energization of relay 52, and therebycontrolling the supply f current from the power supply lines to thetransmitter 6 comprises the monitoring system denoted generally at 60 inthe drawings. 'I'hismonitoring system comprises an antenna 6| which isdisposed in such relation to the transmitting antenna 1 that it receivesenergy therefrom when the transmitter is energized; Current received byantenna 6I is supplied to the grid of a vacuum tube rectifier 62. Amonitor powersupply unit 63 is connected across the main supply linesI4, I and the output of the power supply unit is adapted to provide gridbias current to the tube 62 through potentiometer 64. The monitor powersupply unit 63 also supplies power to the cathode So long as proper,predeterminedput circuit of the tube is connected by lead 66 to thewinding 61 of a relay denoted generally at 66, such relay includingcontacts denoted generally by mnneral 69. A condenser 65 is provided inthe output or plate circuit of the tube to by-pass the alternatingcurrent component of the output of the tube. The relay contacts69preferably comprises two fixed spaced contact'members 15 and 16, both.of which are connected to main power supply line I5 through leads 1Iand 18 respectively, switch 12 and armature 25 of timedelay relay 26.ABetween the xed contacts 15 and 16 and adapted to engage either of themis a movable contact member 11 the movement of which is controlled bythe relay 68. The movable contact member 11 is connected by lead 15 toone terminal of the winding 55 of relay 52, the other Vterminal of thewinding being connected to main power supply line I4 at point I3. 'I'hearrangement of the relay 68 and the contacts is such that relay contactmembers 16 and 'I1 are normally held apart by relay 68 and are adaptedto be closed by some means, such as a spring, when the current inwinding 61 of relay 68 falls below a pre-determined value. The switchmembers 15, 11 are normally held apart by some means, such as a spring,and are adapted to be closed by relay 68 when the current in winding -61exceeds a predetermined value.

The operation of the monitoring system 66 is such that the modulatedcarrier radiated by antenna 1 is received by antenna 6I and rectified bytube 62. The alternating current component of the carrier output of thetube is by-passed through condenser 65, while the direct currentcomponent of the carrier output of the tube ows through the winding 61of sensitive relay 68. The potentiometer 64 may be adjusted so that thegrid bias on the vacuum tube is slightly less than that required forplate current cut-off with a denite carrieramplitude. The realy 61 willtherefore hold the movable contact member 11 in such position that itdoes not engage either of the fixed contact members 15 or 16, this beingthe normal operation of the monitoring. system 60 during properpredetermined operation o! the transmitter 6. So long as the contacts ofrelay 69 are maintained in open position, as described, the circuitthrough winding 55 of relay 52 will be open and the relay contacts 53,54 will therefore remain closed in order to permit the supply of currentfrom main power supply lines I4, I5 to transmitter 6. This conditionwill obtain so long as the current received by'antenna 6| does not fallbelow or exceed predetermined minimum and maximum values and whichcondition will exist so long as the transmitter 6 is supplying a properpredetermined amount of current to antenna 1. When, for any reason, thesupply of current to antenna 1 falls below a predetermined minimum orexceeds a predetermined maximum value, the antenna 6I will receive animproper amount of energy and the supply of current to winding 61 ofrelay 68 will increase or decrease above or below the predeterminedlimits, thereby permitting one of the relay contacts 69 to close. Whentl-s occurs the winding 55 of relay 52 will be connected across the mainpower supply lines I4, I5, the relay 52 will be operated andthe relaycontacts 53, 54 will be opened, thereby disconnecting the transmitter 6from the main power supply line I4, I5. In will be seen that due to suchoperation the eld radiated by antenna 1 will be proper for providing apath to ground at all times when the transmitter is operating and thatwhen the radiated field from antenna 1 provides an improper path togroundthe transmitter 6 will be automatically de-energized.

Means are provided by the present invention for indicating the conditionof energization or deenergization of transmitter 8 and such meanscomprises the signal 80. which is preferably a red visual signal forindicating that the transmitter or the monitoring system therefor is notoperating and the signal 8|, which is preferably a green visual signal,for indicating that the transmitter is properly energized and that themonitoring system therefor is functioning. One terminal of each ofsignals 80 and 8| is connected by lead 39 to main power supply line I5at point I2. The other terminals of signals 8l) and 8| are connectedrespectively to two fixed spaced contact members 82 and 83. Betweencontacts 82 and 33 is arranged a movable contact member 84 which isconnected to main power supply line I4 through lead 49 and whichlnormally engages red signal contact 82 but which is movable intoengagement with either of contact members 32 or 83. The movable contactmember 84 comprises one element of a relay 85 which includes also thewinding or solenoid B6 which, when energized, operates the movablecontact 84 into engagement with green signal contact 83. One terminal ofwinding 86 is connected through lead 81, switch 12 and armature 25 oftime-delay relay 2B to the main power supply line l5 at point I2. 'I'heother terminal of winding 86 is connected through lead 88, lead 50 andswitch 53 to the main poweJl supply line I4 at point I3.

It will be seen that, if the switch 5S is closed, current will besupplied to transmitter 6 when the main power supply lines I4, I5 areconnected to a source of electric energy. Simultaneously, the red signal80 will be energized, due to the fact that movable contact 84 isnormally in engagement with fixed contact 82 and the circuit throughrelay 85 is not yet completed by operation of timedelay relay 35. Theenergization of the red signal 88 at this time indicates that themonitoring system is not yet operating to control transmitter 6. Afterapredetermined interval following the connection of lines I4, I5 topower, the timedelay relay 23 will operate, thereby connecting lead 81to power line I4 through switch 12 and' armature 25 and therebyenergizing relay 85. Movable contact 84 will now be moved out ofengagement with red signal contact 82 and into engagement with greensignal contact 85, thereby energizing the green signal 8| to indicatethatthe transmitter 6 and the monitor therefor are operating properly.

^ Any de-energization of transmitter 6, such as by automatic operationof relay 52 because of improper radiation from antenna 1, or by manualoperation of switch 5B, will break the circuit through relay 85, therebycausing movable contact 84 to move from engagement with green signalcontact 83 into engagement with red signal contact 82, to therebyindicate that the transmitter 6 is de-energized or that the monitortherefor is not functioningproperly.

In the operation of the above described system, when power is connectedto the lines I4, I5 and the switch I6 is closed the transmitter 4 willsupply modulated carrier t the antennas 2, 3 and the radiation fields ofthese antennas will overlap to deiine an equi-signal zone providing arunway localizing beacon. The plates 3|, 32 which are respectivelyarranged locally and capacitatively with respect to the antennas 2, 3,will receive energy from the radiations from antennas 2, 3 and willsupply current to the circuits connected to relays 2|, 22. So long asthe energy supplied to plates 3|, 32 due to the radiated elds ofantennas 2, 3 does not fall below or exceed certain predetermined valuesthe relays 2|, 22 will maintain the contacts 2|a, 22a open therebyde-energizing the winding I9 and permitting the. switches I1, I8 toremain closed. In this condition current will be supplied to transmitter4 from the main power supply line |4, I5 and the green signal 4| will beenergized to show that the transmitter 4 is operating properly. When theenergy introduced into either or both of plates 3 I, 32 falls below apredetermined value the relay 2| will operate to release contact 2 lathereby causing relay |9 to be energized to open contacts I1, |8 anddisconnect the transmitter 4 from the main power supply lines. When theenergy introduced into either or both of the plates 3|, 32 exceeds apredetermined value, the relay 22 will be so operated as to closecontact 22D, thereby energizing relay I8 and causing contacts I1, I8 tobe opened, to disconnect the transmitter 4 from the powervsupply lines.In either of these events the circuit through relay 45 will be openedand the red signal 40 will be operated to indicate that thetranstherefore energize relay 68 in such a manner as to normally holdrelay 69 in open position, thereby disconnecting winding 55 of relay 52from the power supply lines and thereby permitting the contacts 53, 54to remain closed whereby the transmitter 6 is connected to the mainpower supply lines. When the radiation field of antenna 1 falls below apredetermined value the currents supplied to the tube 62 by antenna 6Iwill decrease in such an amount that the output of tube 62 will beinsufiicient to permit the relay 68 to hold switch 69 in open positionand the movable contact 11 will move into engagement with contact 16,thereby connecting winding 55 of relay 52 to the main power supplylines. When the radiated field of antenna 1 exceeds a predeterminedyvalue, the output of tube 62 will increase to such an extent as to movethe contact member 11 into engagement with the fixed contact 15, therebyenergizing relay 52. When the relay 52 is energized the contacts 53, 54will be opened thereby disconnecting transmitter E from the main powersupply lines. At the same time the circuit tnrough winding 86 of relay85 will be broken and the green signal 8| will be de-energzed, while thered signal 8D will be operated to indicate that the transmitter 6 is notoperating.

From the above description of the construction and operation of thesystem accordingr to this invention, it will be seen that there has beenprovided means for insuring that the operation and disposition of theelements of the landing system are prop'er to afford a correct pathalong the runway and a correct curved path to ground, along both ofwhich a landing aircraft may travel in order to descend to ground.Inasmueh as the transmitter will be de-energized in the event ofimproper paths being set up by the radiations from the antennasenergized by the transmitter, it will be apparent that the pilot of alanding aircraft, knowing this, may safely assume that by following theinstrument indications in the aircraft he will follow a correct path toground and may safely land the aircraft.

It will be apparent that different types of relays other than thoseillustrated in Fig. 1 may be employed, and that relays of the typeillustrated at 2|, 22 in Fig. 1 may be used in place of that illustratedat S0, and vice versa.

The monitoring system disclosed hereinbefore and illustrated in Fig. 1of the drawings is particularly, but not exclusively, adapted to thecontrol of beacons of the visual or double-modulation type, in which twocontinuous, characteristic radiations are transmitted. If a beacon ofthe aural type is employed, two non-continuous signals will betransmitted, such as the letter A or a dash from one antenna and theletter I or a dot from the other antenna. If radiations of this type areemployed it will be seen that the noncontinuous currents which will beset up in the relays 2| and 22 of Fig. 1 will cause the relays tooperate or release, thereby closing the circuit through the relay I9 anddisconnecting the transmitter from the source of power.

Means are provided by the present invention for controlling theoperation of an aural beacon to insure that the equi-signal zoneestablished thereby maintains predetermined directional and spatialcharacteristics. A relay controll means of this type is illustrated inFig. 2 of the drawings and comprises the two receiving antennas |00, |0|which may be arranged locally and inductively with respect to thetransmitting antennas 2, 3, and preferably respectively in thedirections of maximum radiation therefrom.

If the antenna |00 is coupled to the antenna which transmits the dot orI signal, it will be apparent that current will flow in antenna |00 onlyduring the successive short intervals of time during which the dot or Iis being transmitted, and that at other alternate intervals no currentwill flow in antenna |00. Antenna |00 is coupled to an oxide rectier|02, the output terminals of which supply current during the periods oftransmission to the winding |03 of a relay |04. The relay |04 comprisestwo fixed contacts |05, |06 and a movable contactI |01 which is movableinto engagement with either of the fixed contacts. One fixed contact |05is connected, through a resistance |08, to the winding |09 of a relayH0, which corresponds in function and operation to the relay 2| ofFig. 1. The

second fixed contact |06 is connected through a battery i to the secondterminal of the winding |00 of relay M0. The movable contact |0lisconnected to the resistance |08 through two series-connected condensersH2, H3, the lead between which is connected to the battery and relaywinding |00.

In the operation of the relay control means described, the movablecontact |077 is connected so that when current due to the transmissionof a dot or I from antenna 2 flows in antenna |00, the movable contact'|0'l will be moved into engagement with fixed contact |05, therebycausing battery to charge condenser |93. Upon discontinuance of thetransmitted signal the movable contact |0l returns to engagement withfixed contact |05, disconnecting the battery and condenser H0 andconnecting the two condensers to cause the charge on condenser H3 to bedistributed between the two. At the same time the f1 charge on the twocondensers flows through relay f coil |09 is maintained at a suihcientlylarge value l to hold open the contacts of relay l0 during the timeelapsing between successive operations of the relay |00, that is, duringthe time during which the antenna is ,deenergized Condenser i i2 andresistor |08 are proportioned so that the current flow through relaycoil |00 will be maintained during the short interval that the antennaand hence relay |06 is energized and condenser ||3 is being charged bybattery The charge on condensers H3 and H2 is thus replenished each timethe relay |04 operates.

The construction and arrangement of the second relay control means ofFig. 2 is similar to that described above, with the exception that theconnections of the fixed contact members |20, l2! thereof are reversedso that when no current flows in antenna |0| during the relatively shortperiods between transmission of an A or dash signal, the battery |22 isconnected to condenser |23 and charges the same. During reception of theA or dash signals the movable contact will engage the fixed contact |2|,thereby causing the charge on condenser |23 to be distributed betweenthe two codnensers. The charges on the two condensers willsimultaneously leak through the coil of' relay |24 to maintain the relaycontacts |25 open.

The above described system provides a means for employing alternatelythe non-continuous energy received from radiated dot and dash or othernon-continuous characteristic signals and energy supplied by a localsource to continuously operate relays. Proper'adjustment of the relaysand circuit constants of Fig. 2 may be made for any type ofcharacteristic non-continuous radiated signals to insure that the relayswill be continuously operated.

After proper adjustment of the relays, any variation in the character ofthe signals transmitted will disturb the operation of the control meansdescribed so that the relays ||0 and |25 will not be continuouslyoperated, thereby operating the relay I9 as described hereinbefore anddisconnecting the transmitter from the source of power. Accordingly, thecontrol means described will insure that the fields radiated by antennas2, 3 will maintain predetermined spatial and directional characteristicsor the transmitting means radiating such fields will be de-energized. l

In the event that it is desired tol receive the radiated fields at apoint or points distant from the source of radiations, the meansdisclosed in Fig. 3 of the drawings may be employed. A receiver |50 isprovided, preferably at the remote point in the radiated fields, andsuch receiver is supplied with energy due to the radiated elds and whichis collected by antenna |5|. The received energy, which will be due toboth radiated fields, in the event that two or more radiated fields havebeen established, is supplied to two electro-mechanical frequencyselectors |52, |53, such as reed converters, which are respectivelytuned to the radiated modulation frequencies. The outputs of the twofrequency selectors are supplied respectively to two rectifiers, theoxide rectiers |50, |55 being illustrated n the drawings. Theserecti'fle'rs each supply a lirect current of a strength proportionalrespecively to the amplitude of the received modulaion frequencies, torelays |56, |51 which corre- :pond in function to the relays 2|, 22 ofFig. 1. if desired, any of the elements illustrated in ig. 3, with theexception of the antenna and eceiver, may be arranged at the remotestayion in the radiated fields and removed from the ;ource ofradiations. Preferably, however, the mtenna and receiver only areremoved from the aource, the other elements being disposed at the:ontrol point and connected to the remotely disnosed antennaand receiverby wires |58, 59.

It will be apparent that the monitor system llustrated in Fig. 3 willoperate to control the aeacon transmitters in the same manner as thesystem illustrated in Fig. l. If two intersecting fields, modulatedrespectively by audio frequen- :ies of 65 and 86.7 cycles are beingradiated, the frequency selectors |52 and |53 will be tuned to 3hoseaudio frequencies and such selectors will :ause currents to flow in therelays |56, |51 which will be proportional to the amplitudes of the re-:eived audio frequencies. So long as the ampli- `nudes of the-neceivedaudio frequencies remain within predetermined limits, the currentssupplied to relays |56, |51 will be proper to-prevent the engagement ofthe movable and xed relay sontacts, thereby permitting continuedAoperation of the transmitters establishing the radiated field which isbeing received. If the received modulation frequencies, and consequentlythe outputs of the frequency selectors and the currents in the relaysvary either above or below the predetermined limits, the relays |56, |51will be operated or released to eiect the de-energization of thetransmitters in the manner described in connection with Fig. 1 of thedrawings.

While certain types of relays have been illustrated in the drawings anddescribed'in the speciflcation, it will be apparent Vthat various typesmay be employed without departing from the scope of the invention andthat any type of relay, which will operate to perform the desiredfunctions may be employed.

While certain forms of my invention have been described and illustrated,it will be apparent to those skilled in the art that modiiications,changes, and improvements may be made in the disclosed forms withoutdeparting in any way from the spirit or scope of the invention, for thelimits of which reference must be had to the appended claims.

We claim:

l. In a radio landing system, means for establishing a radiated eldproviding a radio path to ground having a predetermined shape anddisposition, and means responsive to the intensity of said radiated eldand operable in response to variation of the intensity thereof frompredetermined upper and lower limits for de-energizing the means forestablishing said eld.

2. A radio system comprising transmitting means for establishing aradiated field in space, means for receiving said radiated iield; andmeans constantly controlled and operated by energy received from saidtransmitting means and normally operable to maintain said means forestablishing said field in an energized condition and operable inresponse to variation of the received energy from predetermined upperand lower limits for de-energizing said transmitting means.

3. In a radio landing system, means for radiati ing two intersectingelds defining a path in space having predetermined directionalcharacteristics, receiving means arranged' locally with respect to saidradiating means and adapted to separately receive said two radiatediields, and means controlled by the current received by said' receivingmeans from said two radiated elds and operable to de-energize lsaidradiating means in response to variation of said received current fromupper and lower predetermined limits.

4. A radio system comprising means for transmitting directively twoindependent characteristic modulations dening a zone of equal signalintensity providing a directional guide for a mobile receiving' stationand having predetermined directional characteristics, means for scp-varately receiving and detecting said two characteristic modulations toprovide two currents which are respectively proportional to theamplitudes of said two characteristic modulations, and means controlledby said two currents and normally operable to maintain said transmittingmeans in energized condition and operable in response to variation ofeither of said two currents from predetermined upper and lower limitsfor de-encrgizing said transmitting means.

5. In a radio landing system comprising transmitting means adapted toradiate a field dening a line of constant eld intensity in spaceproviding a path to ground, means for receiving and detecting saidradiated iield to provide a current which is proportional to thestrength of said radiated field, and means controlled by said currentand normally operable to maintain said transmitting means in energizedcondition and operable to de-energize said transmitting y,means inresponse to variation of said current from predetermined upper andlowerlimits.

6. A radio landing system comprising transmitting means for radiating afield in space having predetermined characteristics, means forindicating when 'said transmitter is operating,

means for receiving said radiated field tov provide a received current,means operable by said current to de-energize said transmitting means inresponse to variation of said received current from predetermined upperand lower limits, and means controlled by said de-energizing means forde-energizing said indicating means and for indicating that saidtransmitting means is not operating.

7. A radio system comprising means for transmitting directively twoindependent characteristic modulations, means for receiving saidmodulations to .provide two received currents each being respectivelyproportional to the amplitude of one of said radiated modulations, asource of power and relay means controlling the connection of saidtransmitting means to said source of power, a plurality of relay meanscontrolled by said received currents, each of said plurality of meansbeing connected to control the operation of saidrst-named relay means tocause said first-named-relay means to disconnect said transmittingmeansfrom said source of power in response to variation of said receivedcurrents from predetermined upper and lower limits.

8. A controi means for a radio] transmitting system comprising aplurality of radiating means establishing a plurality of i'lelds whichco-operate in space to produce a path having predetermined directionalcharacteristics, means arranged locally with respect to each of saidradiating means and capacitatively coupled thereto for separatelyreceiving said radiated fields to characteristic non-continuous signals,means for receiving said signals. means for employing the receivedenergy due to said signals for operating a relay and for storingelectric energy, and

lmeans operable during discontinuance of said signals for operating saidrelay by means oi' the stored energy, and means controlled by said relayfor normally maintaining the energization of said radiating means andoperable upon variation of said received energy above or belowpredetermined limits for de-energizing said radiating means. l

10.k A control means for a radio transmitting system comprising meansfor radiating a directional field having impressed thereon acharacteristic non-continuous signal, means for receiving Said signal, acircuit for storing electric energy, a source of power, means controlledby energy fromsaid storage circuit and normally operable thereby tomaintain said radiating means connected to said source of power, meansoperable in response to the reception of said signais 4during periodswhen said signal is radiated for supplying electric energy to saidstorage circuit to replenish energy drawn therefrom, and means operablein response to variation of the current in said receiving means from apredetermined limit for disconnecting said radiating means from saidsource of power.

11. A radio, system comprising two antennas,

means for supplying, said antennas with currentsv f at radio frequencyto thereby establish radiation elds about said antennas, separate meansdisposed in receiving relation with respect to each 'of said antennasfor receiving said radiation ilelds, means for producing from radiationsreceived by said separate means two currents which are respectivelyproportional to the currentsiiow-` ing in said antennas, and meansAcontrolled by said currents and operable to de-energlze said antennas inresponse to variation of either of said currents, from pr-determinedupper and lower limits.

12. A radio system comprising means for establishing av plurality ofintersecting radiated elds, means arranged within each of said radiatedelds and adapted to separately receive said radiations, rectifying meansfor producing from each of the received radiations a current from whichthe carrier component of the received radiation has been eliminated andwhich consists oi Ithe modulation frequency impressed on the carrier insaid field, other rectifying means for producing from each of saidcurrents a current from which the modulation frequency has beeneliminated and which is proportional in strength to the amplitude of themodulation frequency impressed upon the carrier radiated in therespective radiated field, and means controlled by said last-namedcurrents and operable in response' to variation of either of saidlastnamed currenm from upper and lower pre-deterhmined limits Vforde-energizing said radiating means.

13. A radio system comprising transmitting means including a pluralityof antennas and means for energizing said antennas to'produceintersecting radiated elds having lpredetermined directionalcharacteristics. a plurality of receiving means each of which isarranged in such relation to one of said antennas as to receive theradiations therefrom and is disposed in the direction of maximumradiation therefrom and is adapted to have induced therein currentsproportional to the currents flowing in the associated antenna, meansfor producing from the currents induced in said receiving means aplurality of direct currents each of which is proportional in strengthto the current owing in one of theantennas, and means controlled by saiddirect currents for maintaining said transmitting means in energizedcondition while the strengths of said direct currents remainwithinpredetermined limits, said last-named means being operable todevenergize said transmitting means in response to variation of eitherof said direct currents from pre-determined upper and lower limits.

14. A control means for a radio transmitting system comprising means forradiating a directional field having impressed thereon a characterlsticnon-continuous signal, means for receiving said signal, a circuit forstoring electric energy, a-source of power, means controlled by currentfrom said storage circuit and normally operable thereby to maintain saidradiating means connected to said source of power, means operable inresponse to de-energi'zation of said receiving means for supplyingelectric energy to said storage circuit to replenish energy drawntherefrom, and means operable in response to variation of said receivedcurrent from a pre-determined limit for disconnecting said radiatingmeans from said source of power.

15.- A control means for a radio transmitting system comprising meansfor radiating direc-v tional flelds having alternately transmitted noncontinuous signals impressed thereon and which elds overlap in space toprovide an equisignal course havingv pre-determined directionalcharacteristics,v means for separately receiving said radiated nelds, asource of power, a plurality of storage circuits, means controlled bycurrent from said storage circuits and normally operable thereby tomaintain said radiating means connected to said source of power. meansoperable in response to energization of one of said receiving means forsupplying electric energy to one of lsaid storage circuits forreplenishing energy drawn therefrom, meansv operable in response tode-energization of another of said receiving means forY supplyingelectric energy to another of said storage circuits for replenishingyenergy drawn therefrom, and means operable in response to variation ofthe current in either of said receiving means from a pre-determinedlinut established for each "current for disconnecting said radiatingmeans form said source of power.

16. A radio system comprising transmitting means adapted to establishtwo radiated nelds, means connecting said transmitting means to a`source of power, means'arranged in receiving reeach controlled by oneci said currents and each being operable to operate said connectingmeans to disconnect said transmitting means from the source of power inresponse to variation from predetermined upper and lower limits of thecurrent which controls it.

thereby produce in each of said receiving' means a current which isproportional in strength to the corresponding received radiation, andseparate means each of which is controlled by the current produced inone of said receiving means and being normally operated thereby tomaintain said transmitting means in energized condition and beingoperable thereby in response to variation of either of said radiatedelds from predetermined upper and lower limits for de-energizing said 10transmitting means.

GERALD H. WINTERMUTE. GOMER. L. DAVIES.

